The present invention relates to the art of industrial controllers, and more particularly to a method and apparatus for remote paging in a distributed control system.
Industrial controllers are special purpose computers used for controlling industrial processes, manufacturing equipment, and other factory automation applications. In accordance with a control program, an industrial controller may measure one or more process variables or inputs reflecting the status of a controlled process, and change outputs effecting control of the process. The inputs and outputs may be binary, (e.g., on or off), as well as analog inputs and outputs assuming a continuous range of values. The control program may be executed in a series of execution cycles with batch processing capabilities.
The measured inputs received from a controlled process and the outputs transmitted to the process generally pass through one or more input/output (I/O) modules. These I/O modules serve as an electrical interface between the controller and the controlled process, and may be located proximate or remote from the controller. The inputs and outputs are recorded in an I/O table in processor memory. Input values may be asynchronously read from the controlled process by one or more input modules and output values are written directly to the I/O table by the processor for subsequent communication to the process by specialized communications circuitry. An output module may interface directly with a controlled process, by providing an output from an I/O table to an actuator such as a motor, valve, solenoid, and the like.
During execution of the control program, values of the inputs and outputs exchanged with the controlled process pass through the I/O table. The values of inputs in the I/O table are asynchronously updated from the controlled process by dedicated scanning circuitry. This scanning circuitry may communicate with input and/or output modules over a bus on a backplane or network communications. The scanning circuitry also asynchronously writes values of the outputs in the I/O table to the controlled process. The output values from the I/O table are then communicated to one or more output modules for interfacing with the process. Thus, the processor may simply access the I/O table rather than needing to communicate directly with the controlled process.
An industrial controller may be customized to a particular process by writing control software that may be stored in the controller""s memory and/or by changing the hardware configuration of the controller to match the control task. In distributed control systems, controller hardware configuration is facilitated by separating the industrial controller into a number of control modules, each of which performs a different function. Particular control modules needed for the control task may then be connected together on a common backplane within a rack and/or through a network or other communications medium. The control modules may include processors, power supplies, network communication modules, and I/O modules exchanging input and output signals directly with the controlled process. Data may be exchanged between modules using a backplane communications bus, which may be serial or parallel, or via a network. In addition to performing I/O operations based solely on network communications, smart modules exist which may execute autonomous logical or other programs.
Various control modules of a distributed industrial control system may be spatially distributed along a common communication link in several racks. Certain I/O modules may thus be located in close proximity to a portion of the control equipment, and away from the remainder of the controller. Data is communicated with these remote modules over a common communication link, or network, wherein all modules on the network communicate using a standard communications protocol.
In a typical distributed control system, one or more I/O modules are provided for interfacing with a process. The outputs derive their control or output values in the form of a message from a master or peer device over a network or a backplane. For example, an output module may receive an output value from a processor, such as a programmable logic controller (PLC), via a communications network or a backplane communications bus. The desired output value is generally sent to the output module in a message, such as an I/O message. The output module receiving such a message will provide a corresponding output (analog or digital) to the controlled process. Input modules measure a value of a process variable and report the input values to a master or peer device over a network or backplane. The input values may be used by a processor (e.g., a PLC) for performing control computations.
Conventional control devices typically provide a run mode wherein a module executes a control program and a configure mode wherein the control program execution is suspended. As control systems become more widely distributed, the logic or control program associated with a particular process or system may be executed on a large number of modules or devices. In this way, individual processors in the devices execute a program autonomously from the rest of the system components. Smart devices, such as I/O modules, transducers, sensors, valves, and the like may thus be programmed to execute certain logical or other programs or operations independently from other such devices.
In distributed control systems, it may be desirable to notify remote systems or personnel of certain process conditions. Telephone lines and modems may be used to provide communications between controllers in a distributed control system and other devices. In addition, modems and pagers may be used to generate and transmit messages across telephone lines. Conventional modems communicate across telephone lines via standard protocols, such as the Telocator Alphanumeric Paging Protocol (TAP). The modem may communicate with a host device, such as a personal computer, via a standard communications or COMM port using standard communications protocols. The universal applicability of conventional modems is achieved in part through the use of standard communications with personal computers and the like. However, the messaging capabilities of these standard communications protocols is limited with respect to communicating with industrial control devices.
Industrial control devices typically are provided with communications interfaces allowing communication with other devices across a bus or network. Proprietary or specialized communications protocols and messaging are used in such control system communications architectures. Previously, industrial control devices had to be customized in order to communicate with conventional modem devices using standard communications protocols. This increased the cost of the control device, and sacrificed many advantageous messaging capabilities not supported by the standard protocol of prior modems or pagers. Consequently, the application of conventional modems and pagers to industrial control system devices has heretofore failed to adequately provide full communications messaging capabilities between distributed control system devices and remote devices and/or personnel at minimal cost, and without modification of the control system devices.
In accordance with the present invention, there is provided a modem apparatus adapted to provide full messaging and communications interface between a control device and a remote device via a telephone line or other communications medium. The modem includes an interface adapted to communicate directly with a control system device, such as a programmable logic controller (PLC), using a communications protocol compatible with the normal network or backplane communications used in a distributed control system. This apparatus advantageously interfaces directly with unmodified control system devices, providing the ability to send and receive messages from remote devices or personnel via telephone lines or other suitable communications mediums (e.g., Internet, wireless). The employment in the modem of a communications protocol adapted for communications with a control device allows full messaging capabilities between the control device and remote personnel and/or devices.
The apparatus may further be operative to monitor certain control conditions via communications with the control device, and to create and transmit one or more pager messages across telephone lines according to the monitored control conditions. In addition, the apparatus may provide data values in the pager messages to apprise the recipient of process related information relevant to the control condition which initiated the pager message transmission. In addition to the communications protocol compatible with the normal network communications used in a distributed control system, the apparatus may also support standard communications protocols used in conventional modems or pagers. In this regard, a switch or other selection mechanism may be included for user selection of the desired communication protocol. Thus, the modem apparatus may communicate directly with a personal computer or other standard device, whereby the apparatus may be conveniently configured by a user.
In accordance with one aspect of the present invention, there is provided a communications apparatus for communicating with an industrial control device and a remote device via a communications medium. The apparatus includes a first communications interface operative to communicate with the industrial control device using a first communications protocol, a second communications interface operative to communicate with the remote device via the communications medium using a second communications protocol, and a processor in electrical communication with the first and second communications interfaces and operative to exchange messages with the industrial control device and the communications medium via the first and second communications interfaces.
The processor may receive trigger information from the industrial control device via the first communications interface, and selectively construct and transmit one or more pager messages via the second communications interface according to the trigger information.
The communications apparatus may advantageously be programmed or adapted to page remote devices and/or personnel, for example, when a process variable associated with a controlled process exceeds a certain value. According to another aspect of the invention, the first communications protocol may be the Allen-Bradley DF1 protocol and the second communications protocol may be the Telocator Alphanumeric Paging Protocol (TAP). The apparatus thus provides a pager interface with full messaging capabilities for interacting with standard control devices, for example, Allen-Bradley PLC, SLC, Contrologix, and Micrologix processors.
In accordance with another aspect of the present invention, the communications apparatus may further comprise a switch in electrical communication with the processor. The switch may be used to select a communications protocol for the first communications interface. This allows the device to selectively communicate with a control device using one communications protocol (e.g., Allen-Bradley DF1 protocol), or with a programming device (e.g., a personal computer) using another protocol (e.g., ASCII). A user may accordingly program the communications apparatus using a computer, then change the switch position and connect the apparatus to a control device. This aspect of the invention allows the use of the pager or modem communications apparatus with devices supporting disparate communications protocols (e.g., a personal computer and a control device), without the need to modify or customize one of the devices.
According to another aspect of the invention, the communications apparatus may be further adapted to receive programming messages from the communications medium via the second communications interface. This allows the apparatus to be programmed via a programming message from a programming device connected to the communications medium. Thus, the communication device""s program may be changed by remote devices or personnel without interrupting the connection between the apparatus and a control device. This is useful, for example, where a process condition has been reported via the communications apparatus (e.g. by transmitting a pager message), such as a high temperature condition, and a remote user wishes to change the value at which the apparatus will provide subsequent pager messages, or to disable future pages altogether.
According to yet another aspect of the invention, the apparatus may be adapted to receive a programming message from the communications medium via the second communications interface and to transmit the programming message to the industrial control device via the first communications interface. This feature allows a remote user to program the control device from a telephone connection.
According to still another aspect of the invention, the communications apparatus may receive a first message from a first device connected to the communications medium via the second communications interface and transmit or forward the first message to the industrial control device via the first communications interface. In addition, the apparatus may receive a second message from the industrial control device via the first communications interface and transmit or forward the second message to the first device connected to the communications medium via the second communications interface. The apparatus may thus operate as a telephone interface between a remote user and the control device. This is useful, for example, where a remote user or device has received a pager message indicating a particular process variable or condition, and wishes to further interrogate and/or reprogram the control device.
In accordance with another aspect of the invention, an industrial control system is provided for controlling a process. The system comprises a modem or pager communications device having a first communications interface operative to communicate using a first communications protocol, and a second communications interface operative to communicate using a second communications protocol. The first communications protocol may be, for example, the Allen-Bradley DF1 protocol and the second communications protocol may be the Telocator Alphanumeric Paging Protocol (TAP).
The system further includes a control device having a third communications interface adapted for removable connection with the first communications interface and operative to communicate with the modem device using the first communications protocol (e.g., the Allen-Bradley DF1 protocol), and an output operative to interface with a controlled process. A communications medium may be operatively connected to the second communications interface to communicate with the modem device using the second communications protocol (e.g., TAP). The control device may be adapted to send trigger information to the modem device, and the modem device is adapted to selectively construct and transmit a pager message via the second communications interface according to the trigger information
According to yet another aspect of the invention a method is provided for sending a message from a control device to a remote device via a communications medium. The method includes obtaining trigger information via a first communications interface from the control device and determining if a trigger condition exists according to the trigger information. If a trigger condition exists, the trigger condition is correlated with a data variable, which is obtained from the control device via the first communications interface. The method further includes creating a pager message including a text string and the data variable, and transmitting the pager message to a remote device via a second communications interface and the communications medium using a second communications protocol.